Speech pauses in speakers with and without aphasia: A usage-based approach.

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Bello-Lepe, S., Mahmood, S., Varley, R., Zimmerer, V. (2024). Speech pauses in speakers with and without aphasia: A usage-based approach. Cortex, 178, 287-298. https://doi.org/10.1016/j.cortex.2024.06.012

When we speak, we can make pauses to emphasize, to give the listener time to reflect, or for other pragmatic/conversational reasons. But most pauses in speech, whether filled (“um …”) or silent, are disruptions. We may struggle with finding a word, or with planning a sentence. We may even struggle to put together a thought. Most pauses happen when our cognition can’t keep pace with our speech rate.

For that reason, we investigate speech pauses to learn more about language as ias we produce it. The presence and duration of pauses reveal when we face additional processing demands, and can inform us about which properties of language matter. For example, we are more likely to make a pause before a complex sentence, or before a verb rather than a noun. Pauses also provide insights into language impairment, for example following stroke. This paper identifies a new relevant variable for understanding pauses in people with aphasia (a language disorder following brain damage) and healthy controls.

This is work carried out by Sebastián Bello-Lepe under my supervision. Putting the final touches on it after he died was extremely difficult for me. It also made me think more about the “bus factor”, about which I am going to talk later in this post.

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Automated profiling of spontaneous speech in primary progressive aphasia and behavioral-variant frontotemporal dementia: An approach based on usage-frequency.

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Zimmerer, V.C., Hardy, C.J.D., Eastman, J., Dutta, S., Varnet, L., Bond, R.L., Russell, L., Rohrer, J.D., Warren, J.D., Varley, R.A. (2020). Automated profiling of spontaneous speech in primary progressive aphasia and behavioral-variant frontotemporal dementia: An approach based on usage-frequency. Cortex, 133, 103-119. https://doi.org/10.1016/j.cortex.2020.08.027

This one took ages to publish. Not only because we kept adding (post-hoc) analyses, but also because I thought the work should appeal to journals to which it ultimately did not.

We looked at language in rare dementias: Primary progressive aphasia, which mostly affects an individual’s ability to use language (we include the three major types, logopenic variant, semantic variant, and non-fluent variant), and behavioral-variant frontotemporal dementia, which primarily causes behaviour and mood change. Data were provided by colleagues at UCL’s Dementia Research Centre.

The fascinating thing about dementia is that, ultimately, each kind has been associated with some language symptoms.

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For people with a language or cognitive impairment, the difference between "know" and "think" can be the difference between understanding and not understanding a sentence.

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Zimmerer, V.C., Varley, R.A., Deamer, F., Hinzen, W. (2019). Factive and counterfactive interpretation of embedded clauses in aphasia and its relationship with lexical syntactic and general cognitive capacities. Journal of Neurolinguistics, 49, 29-44.

Çokal, D., Zimmerer, V., Varley, R., Watson, S., Hinzen W. (2019). Comprehension of embedded clauses in schizophrenia with and without formal thought disorder. The Journal of Nervous and Mental Disease, 207(5), 384-392.

You and your friend get ready for a day trip to the coast. You see your friend pack light clothing and sunscreen. “I know that it is sunny over there,” she says. You check the weather forecast. It is all clouds and rain. “No,” you say. “You just think that it is sunny.”

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Automated analysis of language production in aphasia and right hemisphere damage: Frequency and collocation strength.

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Zimmerer, V.C., Newman, L., Thomson, R., Coleman, M., & Varley, R.A. (2018). Automated analysis of language production in aphasia and right hemisphere damage: Frequency and collocation strength. Aphasiology, 32(11), 1267-1283. DOI: 10.1080/02687038.2018.1497138

People with aphasia rely on more common words, and more strongly collocated word combinations, in spontaneous language production.

In aphasia, the effects that make a word or sentence easier or harder to process become intensified. Words that take milliseconds longer for a healthy speaker may become out of reach after brain damage. Sentences that are a bit more taxing for grammatical systems may become uninterpretable.

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Language formulas - for your convenience.

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Let's say you know about 30,000 words in your language, which, according to some studies, makes you slightly above average. Some of these entries are everyday words, such as "you", "door", or "go". Others are more rare, like "aghast" and "triptychon". Some of these words are easy to access, usually those that we use often and have a more concrete ("dog") than abstract ("democracy") meaning. There is also an effect of "age of acquisition" in that words that we learned earlier in life seem cognitively more anchored. It is difficult to tell this effect apart from frequency of use, since children tend to learn everyday words first.

If your language system works like the majority of language models suggest, it is based on "words and rules". All words, or at least their roots, are stored in a mental lexicon, and when you utter a sentence your system retrieves each needed word and applies combinatorial ("grammatical") principles to generate the utterance. This needs to happen within fractions of a second. Our system must work like this at least to some degree since we can use our word and combinatorial knowledge to generate a virtually infinite number of sentences.

But how often do we need this procedure?

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Grammatical impairment, historical accidents and silver bullets.

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In 1973, the neurologist Eric Lenneberg made two statements about the nature of language: 1) The rule systems described by Noam Chomsky cannot possibly reflect neurological reality. At best, they serve as metaphors for what the biological language system may do. 2) What is called "Broca's aphasia", the language impairment which results from damage to the frontal lobe of the brain and is characterised by very impoverished and non-fluent speech output, is not a disorder of language per se, but of speaking. It seemed obvious that people with Broca's aphasia could understand language, so Lenneberg believed in the consensus at that time that people with Broca's aphasia found it so difficult to produce speech sounds that they would limit their expressions to the bare minimum.

Lenneberg died two years later, too early to see both statements refuted in the mainstream.

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When passives are easier than actives.

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I met WR when I helped set up a recording session in a clinic in Sheffield. I was a PhD student at that time. WR had been diagnosed with primary progressive aphasia, which is a type of dementia that first manifests as a language impairment. WR was a friendly, gentle person who looked young for being 62. His language production was poor. When he spoke, he had the tendency to connect words with "is a" in an ungrammatical manner ("Mary is a holiday is a Turkey"). He preferred using pen and paper, and while his written language was also poor, communication was better through it. There was no sign that WR had problems beyond language. His non-verbal IQ was above average and as far as I can tell he was leading a very active life. At the time we carried out our research, WR's brain showed relatively small signs of degeneration. When Rosemary Varley and I discussed MRI scans with a radiologist at Royal Hallamshire Hospital, he said that if WR had come in with different problems, such as chronic migraine, it may have gone undetected at first glance. But it was there. Scans showed grey matter reduction in frontotemporal areas both left and right.

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Language and Mental Health

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The project website is not ready at the time I publish this, so I would like to talk a bit about the big project for which Rosemary Varley and I at UCL are currently recruiting aphasic and non-aphasic participants in the London area.

Broadly, there are two questions that drive all research on language: first, how does this complex and powerful apparatus work, and second, how does it interact with, or form the basis of, human thought? These questions are inherently related. Whether we are investigating how children learn language or how language changes in dementia, whether we are looking at language in the brain or trying to get computers to make use of it, whether we are interested in how a language changes over time or search for properties of language that never change, all work makes assumptions about the relationship between our ability to use language and our ability to think.

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